a) Field of the Invention
This invention relates to optical head apparatus used in regeneration, etc. of optical recording disks such as CD and DVD types. In more detail, in optical head apparatus, the inventions relates to light-blocking structure toward nonessential light in light emitted from the light source that passes outside the effective diameter of the objective lens and proceeds toward the optical recording disk.
b) Description of the Related Art
In optical head apparatus used in regeneration, etc. of optical recording disks such as CD and DVD types, objective lens having relatively large aperture was used heretofore; however, in recent years, in order to respond to demand for miniaturization and high-speed access, the trend has been to miniaturize and flatten the objective lens and lens holder, while leaving the movable range of the lens holder (movable range of objective lens) unchanged.
Nonetheless, when objective lens and lens holder are miniaturized and flattened to achieve weight reduction, it is possible to increase servo performance, but when the objective lens is moved in the tracking direction, laser light passes outside the effective diameter of the objective lens to reach the optical recording medium, is reflected by the optical recording medium and enters the photo detector. Such nonessential light, even when received by the photo detector, does not contain regeneration information because it has not received modulation from the recording pit; it is not usable in information regeneration, and moreover, gives rise to large offset in the regenerated signal, and becomes the cause of errors such as level changes at the time of information regeneration. Further, nonessential light also causes offset to occur in tracking error signals and focusing error signals.
As a measure to resolve such problems, as shown in FIG. 4, structure has been proposed wherein, by means of attaching ring-shaped light-blocking plate 103 to lens holder 102 retaining objective lens 101, even when objective lens 101 undergoes maximum movement in tracking direction T, unnecessary light does not reach the optical recording medium by passing outside the effective diameter of objective lens 101.
Moreover, in the optical head apparatus disclosed here, light-blocking plate 103 is located orthogonally to optical axis of objective lens 101; light-blocking face 105 of light-blocking plate 103 is coated wih light-blocking paint, or surface-roughening treatment is implemented to scatter light from the roughened surface. Consequently, nonessential light does not proceed toward photo detector by reflection at light-blocking face 105; therefore, error, etc. caused by nonessential light at the time of information regeneration can be prevented.
Problems To Be Solved By The Invention
Nonetheless, light-blocking plate 103 used in conventional optical head apparatus is a large part that surrounds objective lens 101 at the same width all around, thus there is the problem of having an impediment to miniaturization and weight reduction of the optical head apparatus. Further, in light-blocking plate 103 used in conventional optical head apparatus, there is need to coat light-blocking face 105 with light-blocking paint, or implement roughening treatment of the face, consequently, the problem of high manufacturing cost results.